(a) Field of the Invention
This invention is directed to a photo-sensitive and heat-sensitive composition which is devised to be fixed when irradiated with visible light and generate color when irradiated with ultraviolet radiation to thereby produce a high quality image, and a recording element comprising a support and a layer of said composition superposed thereon.
(b) Description of the Prior Art
A considerably large number of photo-sensitive compositions, photo-sensitive and heat-sensitive compositions and image-forming recording elements using said compositions have been widely utilized or proposed up to now. As typical examples, there can be enumerated, for instance, diazo copying materials using alkali media as developers, photographic films using silver salts, etc. However, the above-mentioned photo-sensitive compositions and recording elements are defective in the fact that developers and fixers must be used in order to obtain an image in practice.
As an attempt to eliminate the foregoing defect, accordingly, public attention has been attracted to dry photochemical photo-sensitive compositions and recording elements capable of forming images only with light as described in Japanese Patent Publications Nos. 19161/1968, 40150/1970, 17855/1972, Japanese Laid Open Patent Application No. 12879/1972, etc. For instance, the photo-sensitive composition as described in Japanese Patent Publication No. 19161/1968 comprises (a) a photooxidant such as hexaarylbiimidazole, tetraarylhydrazine or the like, (b) a color-generator such as leuco-pigment, hydrazone or the like and (c) a binary system redox couple comprising an oxidant component such as quinone, ketone or the like and a reductant component such as alcohol, ester or the like or a one component system redox couple such as 1,4-bis (2-methoxyethyl)anthraquinone or the like. The said photo-sensitive composition generates color by light of specific wavelength such as ultraviolet radiation (the color generating reaction is performed by the action of photooxidant and color-generator, and the originally generated color is deactivated permanently, that is, fixed by light of a different wavelength such as visible light (the fixing reaction is performed by the action of said redox couple). The use of the photo-sensitive composition of this type, accordingly, can obtain both positive image and negative image by selecting the sequence of irradiation of ultraviolet radiation and visible light, but is defective in that the fixing sensitivity (non-color-forming sensitivity) is still low. Accordingly, in order to obtain high contrast and clear-cut copies by using the conventional photo-sensitive components there was inevitably needed a long time period of exposure.